Known installation switching devices are used in electrical installations to protect circuits and/or persons. Circuit breakers (CB) interrupt the current flow through the monitored conductor when excessive current flows or when there is a short circuit. For this purpose they include electromagnetic or thermal tripping devices, and one or more switching locks which, when activated by one of the tripping devices, interrupt the current path between the input and output terminals. Residual current circuit breakers (RCD) for the protection of persons are also known. A fault current occurs when the total of the current flowing into the installation is greater than the total of the current flowing out of the installation; the difference flows away to ground as a fault current. RCD circuit breakers include equipment for detecting the fault current. When such a current occurs it causes a tripping device to interrupt the current path between the input and output terminals.
It is known that information can be obtained about the present magnitude of the current flowing through the current path or paths of the switching device through the inclusion of an additional current transformer and an additional source of auxiliary voltage to supply the current transformer. EP 0 750 382 A2 illustrates this arrangement using the example of a low-voltage power switch used to switch off large currents when under load, and which is large in size compared to a usual circuit breaker. For a circuit breaker this solution means that an additional connection is specified for the neutral conductor, and the additional space specified in the device for the source of auxiliary voltage is lost. Such a solution can therefore not be used for circuit breakers, for the practical reason that not much space is available inside circuit breaker housings.
The additional information obtained through the additional current transformer is transmitted to a signal/control unit for monitoring, measurement or supervisory purposes.
As switching devices are increasingly networked in building automation systems, this facility for obtaining information about the magnitude of the current flowing in the current path or paths through the switching device, and of transmitting it to signal/control units for supervisory and monitoring purposes, is becoming more important.
EP 2 282 321 A1 discloses a module for measuring the current flowing in one conductor of a low-voltage distributor. The module containing the current sensor is plugged from the outside onto the housing of a circuit breaker, whereby a fastening tongue on the module is clamped firmly into one of the two terminal chambers in the double-row terminal of the circuit breaker. The increased space specification for the combination of circuit breaker and current measuring module is, however, disadvantageous here, as is the obstruction of one of the two terminal connection chambers, which is no longer available for the connection of, for instance, a power rail.